In a large hull or the like, there may be cases where plural outboard motors are mounted for obtaining larger propulsive force. The outboard motors obtain propulsive force by rotating a propeller, and thus rotation reaction force of the propeller may operate to the hull mounting the outboard motors to cause a side slide. Therefore, when plural outboard motors are mounted in the hull, to suppress the side slide, generally rotation directions of the propellers of respective outboard motors are set in opposite directions, making them for regular rotation and for counter rotation.
In the outboard motor for regular rotation, the propeller rotates rightward when seen in a traveling direction while moving forward, and in the outboard motor for counter rotation, the propeller rotates leftward when seen in the traveling direction while moving forward.
In general, the outboard motor for regular rotation and the outboard motor for counter rotation have different gears for switching the rotation direction of the propeller. This is because required performances are different in terms of use time (durability) and transfer torque (strength) between a gear for moving forward and a gear for moving backward, and is for using gears corresponding to the required performances for the gear for moving forward and the gear for moving backward to thereby reduce production costs. In such a structure, it is necessary to prepare a dedicated propulsion unit (gear case) for each of the outboard motor for regular rotation and the outboard motor for counter rotation. Thus, management of parts is complicated and retail stores always have to stock two types of propulsion units, and this increases management costs and has been a main cause for rise of sales costs.
Regarding such a program, Patent Literature 1 discloses a technology of making the gear case for regular rotation and the gear case for counter rotation as a common unit by similarly structuring a gear for moving forward and a gear for moving backward and also a bearing of the gear for moving forward and a bearing of the gear for moving backward.